Reactions of Group 4 Metallocene Complexes with Mono- and Diphenylacetonitrile: Formation of Unusual Four- and Six-Membered Metallacycles

Reactions of Group 4 metallocene alkyne complexes [Cp-2'M(eta(2)-Me3SiC2SiMe3)] (1: M= Zr, Cp'= Cp*= eta(5)-pentamethylcyclopentadienyl; 2a: M= Ti, Cp'= Cp*, and 2b: M= Ti, Cp-2' = rac-(ebthi)= rac-1,2-ethylene-1,1'- bis(eta(5)-tetrahydroindenyl)) with diphenylacetonitrile (Ph2CHCN) and of the seven-membered zirconacyclocumulene 3 with phenylacetonitrile (PhCH2CN) were investigated. Different compounds were obtained depending on the metal, the cyclopentadienyl ligand and the reaction temperature. In the first step, Ph2CHCN coordinated to 1 to form [Cp-2*Zr(eta(2)-Me3SiC2SiMe3)(NCCHPh2)] (4). Higher temperatures led to elimination of the alkyne, coordination of a second Ph2CHCN and transformation of the nitriles to a keteniminate and an imine ligand in [Cp-2*Zr(NC2Ph2)(NCHCHPh2)] (5). The conversion of 4 to 5 was monitored by using H-1 NMR spectroscopy. The analogue titanocene complex 2a eliminated the alkyne first, which led directly to [Cp-2*Ti(NC2Ph2)(2)] (6) with two keteniminate ligands. In contrast, the reaction of 2b with diphenylacetonitrile involved a formal coupling of the nitriles to obtain the unusual four-membered titanacycle 7. An unexpected six-membered fused zirconaheterocycle (8) resulted from the reaction of 3 with PhCH2CN. The molecular structures of complexes 4, 5, 6, 7 and 8 were determined by X-ray crystallography.